Concentrated aqueous $NaOH$ can separate a mixture of

Among $PbS$,$CuS$,$HgS$,$MnS$,$Ag_2S$,$NiS$,$CoS$,$Bi_2S_3$,and $SnS_2$,the total number of black coloured sulphides is

Which of the following statement$(s)$ is/are correct with reference to $Fe^{2+}$ and $Fe^{3+}$ ions?
$(1)$ $Fe^{3+}$ gives brown colour with potassium ferricyanide
$(2)$ $Fe^{2+}$ gives blue colour with potassium ferricyanide
$(3)$ $Fe^{3+}$ gives red colour with potassium thiocyanate
$(4)$ $Fe^{2+}$ gives brown colour with ammonium thiocyanate

When a salt is treated with sodium hydroxide solution,it gives gas $X$. On passing gas $X$ through reagent $Y$,a brown-coloured precipitate is formed. $X$ and $Y$ respectively,are

When $H_2S$ gas is passed through the $HCl$ containing aqueous solutions of $CuCl_2$,$HgCl_2$,$BiCl_3$ and $CoCl_2$,which does not precipitate out?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$AlCl_3 + Na_3PO_4 \longrightarrow AlPO_4 \downarrow$